There have been a great many attempts at developing devices to provide short pulses of electrical power using mechanical energy. Such devices would be useful for powering equipment such as intrusion alarms where the intruder would provide the mechanical energy to produce the electrical power.
Intrusion alarms and sensors are normally wired to electrical power lines and the outputs are transmitted by electrical conduction to control stations. One alternative, especially used in remote locations, has been to use batteries to power radio frequency transmitters to transmit an alarm signal to a control station. Battery replacement can become a problem.
U.S. Pat. Nos. 3,772,669 and 3,831,157 describe methods attempted to develop pulse power for alarm use. Both patents require large forces (over 15 lbs) to activate them; both are extremely limited in applications (require high leverage, essentially nonconductive door jams), neither has envisioned the need for an alarm encoding to indicate alarm location in a multiple alarm environment, neither is capable of providing bi-directional outputs (i.e., "alarmed" position, and "activated" position), and neither is capable of providing easy application to other uses.
U.S. Pat. Nos. 4,020,369 and 4,118,717, use flux switching to generate electrical pulses for camera use. Both use an inefficient design for generating useful energy. They wrap the induction coil only around one pole piece of the magnet, and use only one polarity sense of the induced voltage. The coil on the pole piece loses efficiency due to all the flux loss paths surrounding the magnet. This design would not be appropriate for intrusion alarm use, even if it were scaled up in energy output, because of the large attractive force which would be required to pull the keeper away from the magnet.
U.S. Pat. Nos. 4,412,355 and 4,480,808 use magnets oscillating past pole pieces containing a coil to generate energy from mechanical inputs. The power being produced will be roughly a sinusoid of frequency corresponding to the oscillations of the magnets. Neither device would provide electrical pulses appropriate for intrusion alarm use.
To effectively operate a wireless intrusion alarm an electrical pulse should provide a peak power of at least 0.1 Watt to provide sufficient RF prime power, and should have a duration of at least 30 milliseconds to provide sufficient time to code the transmission, with a total energy of at least 3 millijoules.